Had a horse I worked a year to get some heal heighth on, the owner wanted a pair of them on. He bought'em, I put'em on. I found they were very hard to shape (must have their special tool to shape), nail holes were full of rubber, hard to set the nails in, and after one setting, the heal heighth I got was worn off. I think if you had really good hooves, maybe ok, but I will never set another pair on.
I know of another farrier here who swears by them. So ????